Known recording methods are based on magnetic or optical read/write (R/W) techniques or a mixture of both. Well-known devices are, for example, the magnetic disk storage, even better known as hard disk, and the magneto-optical disk storage, which recently gained access to the computer market. Another example of an optical device for mass data storage is the so-called compact disk (CD), which belongs to the read only memories (ROMs).
A typical hard disk consists of several disk-shaped substrates covered with one or several layers of magnetic material, e.g. iron oxide, chromium dioxide, or Fe-, Co-, and Ni-alloys. The information is stored and read by a magnetic head which floats within a small distance over the disk. In the case of the conventional magnetic disk systems, the size of the magnetic head and the length of the transition zone, i.e. the distance over which the recording material changes its direction of magnetization, roughly govern the area of a storage element. Such a storage element, in case of magnetic recording devices also known as bit domain, is defined as the area in which the smallest information unit (bit) is stored.
In magneto-optical storage devices, as described, for example, in EP-A-0498459, the change of magnetization is supported by laser radiation. In this case, the size of the storage element is defined by the size of the focal spot on the recording material and, thus, restricted by the wavelength of the laser radiation.
Even higher storage densities, i.e. a larger number or storage elements per unit area, can be achieved by a technique known as spectral hole burning. This technique is described, for example, in U.S. Pat. No. 4,101,976. It uses light-absorbing molecules for data storage. These molecules are imbedded in a matrix which mainly shifts the absorption bands of the molecules. With a large number (10.sup.9) of molecules per storage element involved, the combined absorption bands spread over a relatively large range of wave numbers. It is possible to store information using a laser, the radiation of which has only a small band width compared to the combined absorption bands of the molecules. The ratio of absorption bandwidth over laser radiation band width limits the number of storage elements per laser spot size. Even though it is possible to establish this ratio around 10.sup.3, still approximately 10.sup.6 light-absorbing molecules are serving as one storage element.
Another technique, also working on a molecular level, is described in U.S. Pat. No. 4,032,901. It makes use of natural or artificially synthesised macromolecules, having a size around 10 nm or less, which are deposited as a layer. Small regions of this layer, with lateral dimensions of 100 nm or less, can be selectively modified by a narrowly focussed electron beam without affecting adjacent regions, to store (write) information as a pattern of regions of modified particles. Each region is regarded as a storage elements. After depositing a thin metallic film onto the layer, the stored information is read out by a detecting electron beam. Even those storage devices and techniques which make use of recording material on a molecular scale, still show restrictions concerning the size of the storage element's area. This area is limited by the focal spot of either the laser beam or the electron beam.
Modern electronic equipment, such as computers, microprocessors, laser printers, and even the quickly growing field of digitally processed media, e.g. music and image processing, require large storage capacities for binary coded data. It is, therefore, an object of the invention to provide a new method for storing binary coded data. It is a further object of the invention to provide a method for a recording and reproducing method for media with a high storage density. More specifically, it is an object of the invention to provide a method for using storage elements of molecular size. Another object is to provide a recording or storage medium with a high storage density. A further object of the invention is to provide a recording medium having storage elements of a size which is reducible to the size of the molecules used as recording material.